This invention relates to a catalyst-type exhaust gas purifying device for use in internal combustion engines which are mounted in automobiles or the like.
Heretofore, there have been known many types of exhaust gas purifying devices for removing especially harmful components in an exhaust gas, such as carbon monoxides, non-burnt hydrocarbons and nitrogen oxides, from internal combustion engines. As one type of such devices, there have been known exhaust gas purifying devices utilizing catalysts. As the latter type of devices, there has been generally known a device in which so-called pellet type catalyzers each consisting of a pellet carrier and metal catalyst carried thereon are stratified within a metal housing. In this device, an exhaust gas is passed between the layers of the stratified pellet type catalyzers and is subjected to chemical reaction while being passed therebetween, and thereby made harmless. There has also been known another exhaust gas purifying device in which monolithic catalyzing element consisting of a monolithic ceramic carrier and metal catalyst carried thereto is used, and such purifying device is disclosed in U.S. Pat. Nos. 3,441,381 and 3,441,382. The monolithic ceramic carrier is provided with openings at its respective ends and a plurality of exhaust gas passages defined therein. The device utilizing the monolithic catalyzing element is advantageous as compared with the device utilizing the pellet type catalyzers, from the standpoints that the monolithic catalyzing element is not subjected to wear and deterioration due to its vibration, and that construction of a housing receiving the catalyzing element can be made simple. However, this device has a disadvantage such that the monolithic catalyzing element will collide with the housing due to its vibration transmitted from engine and thereby be damaged, if suitable cushioning materials should not be filled in a space between an inner wall surface of the housing and an outer periphery of the catalyzing element. Because, generally, the difference of heat expansion coefficients between the metal housing and the monolithic catalyzing element is fairly large, so that the space between the inner wall surface of the housing and the outer periphery of the catalyzing element will be considerably expanded when the device is subjected to high temperature. It will be easily understood that such expansion of the space will cause the catalyzing element to vibrate and thereby to collide with the housing.
In order to eliminate aforementioned disadvantage, the device of the U.S. Pat. No. 3,441,381 employs metal fabric filled in a space between the inner wall surface of the housing and the outer periphery of the monolithic catalyzing element as cushioning material. Further, in the device of the U.S. Pat. No. 3,441,382, the monolithic catalyzing element is held by means of a spring through heat insulating material made of ceramic. The device of the U.S. Pat. No. 3,441,381 is effective when it is used under a condition that the metal fabric may not be subjected to high temperature, so that elasticity of the fabric may not be lost. However, in case that the latter device should be used in engines of automobiles or the like, which may be operated under a variety of load conditions, temperature of the metal fabric reaches several hundreds degrees (.degree.C) under high load high rotating operation. When the metal fabric is subjected to such high temperature, it loses its elasticity, so that cushioning effects of the metal fabric may be lost. This leads to damage of the monolithic catalyzing element as previously described. Further, the device of the U.S. Pat. No. 3,441,382 has a disadvantage such that it is complex in construction and will be high in manufacturing cost.